This invention relates to an improved all-purpose liquid cleaner which can be in the form of a microemulsion designed in particular for cleaning hard surfaces and which is effective in removing grease soil and/or bath soil and in leaving unrinsed surfaces with a shiny appearance.
In recent years all-purpose liquid detergents have become widely accepted for cleaning hard surfaces, e.g., painted woodwork and panels, tiled walls, wash bowls, bathtubs, linoleum or tile floors, washable wall paper, etc.. Such all-purpose liquids comprise clear and opaque aqueous mixtures of water-soluble synthetic organic detergents and water-soluble detergent builder salts. In order to achieve comparable cleaning efficiency with granular or powdered all-purpose cleaning compositions, use of water-soluble inorganic phosphate builder salts was favored in the prior art all-purpose liquids. For example, such early phosphate-containing compositions are described in U.S. Pat. Nos. 2,560,839; 3,234,138; 3,350,319; and British Patent No. 1,223,739.
In view of the environmentalist's efforts to reduce phosphate levels in ground water, improved all-purpose liquids containing reduced concentrations of inorganic phosphate builder salts or non-phosphate builder salts have appeared. A particularly useful self pacified liquid of the latter type is described in U.S. Pat. No. 4,244,840.
However, these prior art all-purpose liquid detergents containing detergent builder salts or other equivalent tend to leave films, spots or streaks on cleaned unrinsed surfaces, particularly shiny surfaces. Thus, such liquids require thorough rinsing of the cleaned surfaces which is a time-consuming chore for the user.
In order to overcome the foregoing disadvantage of the prior art all-purpose liquid, U.S. Pat. No. 4,017,409 teaches that a mixture of paraffin sulfonate and a reduced concentration of inorganic phosphate builder salt should be employed. However, such compositions are not completely acceptable from an environmental point of view based upon the phosphate content. On the other hand, another alternative to achieving phosphate-free all-purpose liquids has been to use a major proportion of a mixture of anionic and nonionic detergents with minor amounts of glycol ether solvent and organic amine as shown in U.S. Pat. No. 3,935,130. Again, this approach has not been completely satisfactory and the high levels of organic detergents necessary to achieve cleaning cause foaming which, in turn, leads to the need for thorough rinsing which has been found to be undesirable to today's consumers.
Another approach to formulating hard surfaced or all-purpose liquid detergent composition where product homogeneity and clarity are important considerations involves the formation of oil-in-water (o/w) microemulsions which contain one or more surface-active detergent compounds, a water-immiscible solvent (typically a hydrocarbon solvent), water and a "cosurfactant" compound which provides product stability. By definition, an o/w microemulsion is a spontaneously forming colloidal dispersion of "oil" phase particles having a particle size in the range of 25 to 800 .ANG. in a continuous aqueous phase.
In view of the extremely fine particle size of the dispersed oil phase particles, microemulsions are transparent to light and are clear and usually highly stable against phase separation.
Patent disclosures relating to use of grease-removal solvents in o/w microemulsions include, for example, European Patent Applications EP 0137615 and EP 0137616--Herbots et al; European Patent Application EP 0160762 - Johnston et al; and U.S. Pat. No. 4,561,991--Herbots et al. Each of these patent disclosures also teaches using at least 5% by weight of grease-removal solvent.
It also is known from British Patent Application GB 2144763A to Herbots et al, published Mar. 13,1985, that magnesium salts enhance grease-removal performance of organic grease-removal solvents, such as the terpenes, in o/w microemulsion liquid detergent compositions. The compositions of this invention described by Herbots et al. require at least 5% of the mixture of grease-removal solvent and magnesium salt and preferably at least 5% of solvent (which may be a mixture of water-immiscible non-polar solvent with a sparingly soluble slightly polar solvent) and at least 0.1% magnesium salt.
However, since the amount of water immiscible and sparingly soluble components which can be present in an o/w microemulsion, with low total active ingredients without impairing the stability of the microemulsion is rather limited (for example, up to 18% by weight of the aqueous phase), the presence of such high quantities of grease-removal solvent tend to reduce the total amount of greasy or oily soils which can be taken up by and into the microemulsion without causing phase separation.
The following representative prior art patents also relate to liquid detergent cleaning compositions in the form of o/w microemulsions: U.S. Pat. Nos. 4,472,291--Rosario; 4,540,448--Gauteer et al; 3,723,330--Sheflin; etc.
Liquid detergent compositions which include terpenes, such as d-limonene, or other grease-removal solvent, although not disclosed to be in the form of o/w microemulsions, are the subject matter of the following representative patent documents: European Patent Application 0080749; British Patent Specification 1,603,047; 4,414,128; and 4,540,505. For example, U.S. Pat. No. 4,414,128 broadly discloses an aqueous liquid detergent composition characterized by, by weight:
(a) from 1% to 20% of a synthetic anionic, nonionic, amphoteric or zwitterionic surfactant or mixture thereof; PA1 (b) from 0.5% to 10% of a mono- or sesquiterpene or mixture thereof, at a weight ratio of (a):(b) being in the range of 5:1 to 1:3; and PA1 (c) from 0.5% 10% of a polar solvent having a solubility in water at 15.degree. C. in the range of from 0.2% to 10%. Other ingredients present in the formulations disclosed in this patent include from 0.05% to 2% by weight of an alkali metal, ammonium or alkanolammonium soap of a C.sub.13 -C.sub.24 fatty acid; a calcium sequestrant from 0.5% to 13% by weight; non-aqueous solvent, e.g., alcohols and glycol ethers, up to 10% by weight; and hydrotropes, e.g., urea, ethanolamines, salts of lower alkylaryl sulfonates, up to 10% by weight. All of the formulations shown in the Examples of this patent include relatively large amounts of detergent builder salts which are detrimental to surface shine. PA1 about 3 to about 40 wt. %, more preferably about 5 to about 20 wt. % of an analephotropic negatively charged complex comprising at least one an alkali metal salt or an alkaline earth metal salt of a sulfate or sulfonate anionic surfactant and mixtures thereof being complexed with an amphoteric (zwitterionic) surfactant or a high dipole moment surfactant selected from the group consisting of amine oxides or alkylene carbonates. PA1 0.5% to 10%, more preferably 1% to 7%, of a Lewis base, neutral polymer; PA1 0 to about 15% of magnesium sulfate heptahydrate; PA1 the balance being water, said proportions being based upon the total weight of the composition. PA1 (a) at least one anionic surfactant which is an alkali metal salt or an alkaline earth metal salt of a sulfonate or sulfate surfactant; and PA1 (b) an amine oxide, zwitterionic surfactant or an alkylene carbonate, wherein the ratio of the anionic surfactant to the zwitterionic surfactant or amine oxide is 4:1 to 0.2:1, more preferably 2.5:1 to 0.4:1 and the ratio of the anionic surfactant to the alkylene carbonate is 7:1 to 1.2:1. The instant composition contains about 3 to about 40 wt. %, more preferably about 5 to about 20 wt. % of the analephotropic negatively charged complex.
A pH neutral microemulsion composition based on paraffin sulfonate and ethoxylated nonionic surfactant is able to deliver improved grease cleaning versus built, alkaline compositions. Besides the improved grease cleaning, this approach is much safer to surfaces as well as less aggressive on consumer's hands (Loth et al--U.S. Pat. No. 5,075,026).
The microemulsion technology provides outstanding oil uptake capacity because of the adjustment of the curvature of the surfactant micelles by the molecules of the cosurfactant. Rod-like micelles are preferred as they can "swallow" oil to become globular without increasing the surface of contact between the hydrophobic core of the micelle and the hydrophilic continuous phase.
In diluted usage however, the microemulsion state is usually lost and the cleaning performance relies on the adsorption efficacy and leaving character of the surfactant system. Nonionic surfactants perform very well on grease, as they are excellent grease "solubilizers". Actually, they spontaneously form swollen micelles. In moderate climate countries such as the northern states of the United States and the northern countries of Europe, the soil on the hard surfaces contains a major proportion of greasy materials. It is accordingly not surprising that the anionic-nonionic surfactant based microemulsion is so efficient in those countries. In hot weather countries however, the amount of particulate soils is more important (as doors and windows remain open) and the classical microemulsion (U.S. Pat. No. 5,075,026) shows weaknesses on this type of soil which is a mixed grease-particulate soil in nature.
The instant invention solves this problem by delivering on the solid surface to be cleaned the proper surfactant mixture that best adsorbs on the surface while keeping a good "leaving" character.
The instant invention teaches that all purpose cleaning or microemulsion compositions containing a negatively charged complex of an anionic surfactant with an amphoteric or high dipole moment surfactant deliver this desired property. The analephotropic complex adsorbs much better on grease than on silica surface than individual anionic surfactants alone. This results in enhanced capabilities to disperse complex mixtures of grease with embedded particles of soil which are essential for particulate soil removal.
As illustrated in the examples, it is essential that the complex mixture is negatively charged. Pseudo-nonionic surfactants resulting from anionic-cationic complexes which are not negatively charged show very low particulate soil removal.